1. Technical Field
The present invention relates to an electronic timepiece, and relates more particularly to an electronic timepiece with a planar antenna.
2. Related Art
JP-A-2012-13627 describes an electronic timepiece with a planar antenna for receiving radio frequency signals transmitted from GPS (Global Positioning System) or other types of positioning information satellites.
The electronic timepiece in JP-A-2012-13627 has a planar antenna disposed on the back cover side of the dial, and suppresses loss of antenna sensitivity by separating the planar antenna from the metal case around the antenna.
Disposing the planar antenna closer to the base plate that is also disposed on the back cover side of the dial is desirable to make the electronic timepiece thinner. Because the base plate is made of plastic or other non-conductive material, the base plate does not interfere with radio waves, and the planar antenna can receive radio signals even with the planar antenna disposed adjacent to the base plate.
Because the base plate is a dielectric, however, a new problem of the antenna frequency shifting occurs if the gap between the base plate and the antenna electrode is too small. More specifically, the antenna frequency begins shifting if the gap between the base plate and the antenna electrode of the planar antenna is less than approximately 1.0 mm. The problem becomes particularly acute if this gap is 0.5 mm or less because the frequency shift increases with even the slightest change in the gap between the base plate and the antenna electrode, reception performance drops, and antenna characteristics are not stable.